1. Field of the Invention
This invention relates to a magnetic recording medium and a method of producing the same. More specifically, it relates to a magnetic recording medium of the coated type which has smooth surface properties, has small spacing between head and the medium, enables high-density recording, shows favorable running performance and causes little head wear, and a method of producing a magnetic recording medium whereby the above-described characteristics can be established while achieving a high productivity.
2. Description of the Related Art
In the field of magnetic recording, recording wavelength becomes shorter with the recent increases in the recording density. With the tendency toward using MR heads as reproduction heads, attempts have been made to finely divide a magnetic material and thus increase the number of magnetic particles per unit volume thereby reducing medium noises. To magnetically separate magnetic particles, there has been employed high-dispersion of a magnetic solution. When a magnetic solution is high-dispersed, however, there arises a problem that the exposure of abrasive particles from a magnetic layer is inhibited or the projection height on the magnetic layer surface is lowered and thus the durability is worsened.
To solve this problem and establish both of high-density recording and an excellent run durability, there has been proposed a method wherein diamond having an elevated abrasive power and a controlled particle size is employed as an abrasive (see JP-A-2000-149243 and JP-A-2003-85734).
JP-A-2000-149243 and JP-A-2003-85734 propose a technique of dispersing diamond in a magnetic solution by using a sand mill. However, this method suffers from a problem that the diamond causes abrasion of media beads (for example, glass beads or ZrO2 beads) or the inner wall (mainly made of stainless steel) of the disperser in the course of the dispersion and thus abrasion dusts contaminate the magnetic solution. Therefore, both of high-density recording and an excellent run durability can be hardly established by using the known techniques as described above.
Under these circumstances, the present applicant has proposed a method of manufacturing a magnetic recording medium which comprises separately dispersing a magnetic solution which contains the ferromagnetic powder and the binder, and an abrasive solution which contains an abrasive and a solvent, then mixing the magnetic solution and the abrasive solution together, and after that, subjecting the liquid mixture of the magnetic solution with the abrasive solution to a dispersion treatment by the application of ultrasonic waves (JP-A-2005-228369).
This production method is useful, since a magnetic recording medium suffering from little contamination with foreign matters, having excellent run durability and causing little head wear can be obtained thereby.
To enlarge the recording capacity of a magnetic recording medium, it is required to elevate the recording density. For this purpose, attempts have been made to reduce the particle size of a magnetic material in a magnetic layer and smoothen the surface. Furthermore, there have been proposed anisotropic magnetoresistive heads (so-called AMR heads) and giant magnetoresistive heads (so-called GMR heads) having further elevated sensitivity.
However, it has been found out that, in the case where the surface roughness is extremely elevated by using the technique disclosed in JP-A-2005-228369, there arise troubles such as sticking of a medium to a head and stripping of a magnetic layer due to sliding with a guide.